A direct laser-synthesized magnetic metamaterial for low-frequency wideband passive microwave absorption

Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.

Electrically-driven ultrafast out-of-equilibrium light emission from hot electrons in suspended graphene/hBN heterostructures

Nanoscale light sources with high speed of electrical modulation and low energy consumption are key components for nanophotonics and optoelectronics.The record-high carrier mobility and ultrafast carrier dynamics of graphene make it promising as an atomically thin light emitter which can be further integrated into arbitrary platforms by van der Waals forces.However,due to the zero bandgap,graphene is difficult to emit light through the interband recombination of carriers like conventional semiconductors.Here,we demonstrate ultrafast thermal light emitters based on suspended graphene/hexagonal boron nitride(Gr/hBN)heterostructures.Electrons in biased graphene are significantly heated up to 2800 K at modest electric fields,emitting bright photons from the near-infrared to the visible spectral range.By eliminating the heat dissipation channel of the substrate,the radiation efficiency of the suspended Gr/hBN device is about two orders of magnitude greater than that of graphene devices supported on SiO2or hBN.Wefurther demonstrate that hot electrons and low-energy acoustic phonons in graphene are weakly coupled to each other and are not in full thermal equilibrium.Direct cooling ofhigh-temperature hot electrons to low-temperature acoustic phonons is enabled by the significant near-field heat transfer at the highly localized Gr/hBN interface,resulting in ultrafast thermal emission with up to 1 GHz bandwidth under electrical excitation.It is found thatsuspending the Gr/hBN heterostructures on the SiO2trenches significantly modifies the light emission due to the formation of the optical cavity and showed a~440%enhancement inintensity at the peak wavelength of 940 nm compared to the black-body thermal radiation.The demonstration of electrically driven ultrafast light emission from suspended Gr/hBNheterostructures sheds the light on applications of graphene heterostructures in photonicintegrated circuits,such as broadband light sources and ultrafast thermo-optic phase modulators.

Sparse representation for machine learning the properties of defects in 2D materials

Two-dimensional materials offer a promising platform for the next generation of(opto-)electronic devices and other high technology applications.One of the most exciting characteristics of 2D crystals is the ability to tune their properties via controllable introduction of defects.However,the search space for such structures is enormous,and ab-initio computations prohibitively expensive.We propose a machine learning approach for rapid estimation of the properties of 2D material given the lattice structure and defect configuration.The method suggests a way to represent configuration of 2D materials with defects that allows a neural network to train quickly and accurately.We compare our methodology with the state-of-the-art approaches and demonstrate at least 3.7 times energy prediction error drop.Also,our approach is an order of magnitude more resource-efficient than its contenders both for the training and inference part.

Exploring van der Waals materials with high anisotropy:geometrical and optical approaches

The emergence of van der Waals(vdW)materials resulted in the discovery of their high optical,mechanical,and electronic anisotropic properties,immediately enabling countless novel phenomena and applications.Such success inspired an intensive search for the highest possible anisotropic properties among vdW materials.Furthermore,the identification of the most promising among the huge family of vdW materials is a challenging quest requiring innovative approaches.Here,we suggest an easy-to-use method for such a survey based on the crystallographic geometrical perspective of vdW materials followed by their optical characterization.Using our approach,we found As2S3 as a highly anisotropic vdW material.It demonstrates high in-plane optical anisotropy that is~20%larger than for rutile and over two times as large as calcite,high refractive index,and transparency in the visible range,overcoming the century-long record set by rutile.Given these benefits,As2S3 opens a pathway towards nextgeneration nanophotonics as demonstrated by an ultrathin true zero-order quarter-wave plate that combines classical and the Fabry–Pérot optical phase accumulations.Hence,our approach provides an effective and easy-to-use method to find vdW materials with the utmost anisotropic properties.

Recent Advances in Organic Photocatalysts for Solar Water Splitting

Facing the current energy crisis and climate change,the discovery of robust yet inexpensive photocatalysts that harvest solar energy for overall water splitting is highly desirable.Recently,organic materials have attracted much attention in photocatalysis,attributed to their facile molecular-level functionalization,adjustable optoelectronic properties,favorable chemical robustness,and lesser environmental hazards as compared with their inorganic counterparts.This minireview highlights the recent advances of organic photocatalysts in the field of solar water splitting.The challenges,opportunities,and future perspectives within the field are discussed to inspire future research studies into organic-based photocatalytic water splitting.

A systematic understanding of microbial reductive dechlorination towards an improved“one health”soil bioremediation:A review and perspective

Chlorinated organic pollutants(COPs),both emerging and traditional,are typical persistent pollutants that harm soil health worldwide.Dechlorinators mediated reductive dechlorination is the optimal way to completely remove COPs from anaerobic soil through a redox reaction driven by electron transfer during microbial anaerobic respiration.Generally,the dechlorinated depletion of COPs in situ often interacts with multiple element biogeochemical activities,e.g.,methanogenesis,sulfate reduction,iron reduction,and denitrification.Elucidating the relevance of biogeochemical cycles between COPs and multiple elements and the coupled mechanisms involved,thus,helps to develop effective pollution control strategies with the balance between pollution degradation and element cycles in heterogeneous soil,ultimately contributing to“one health”goal.In this review,we summarized the microbial-chemical coupling redox processes and the driving factors,elucidated the interspecies metabolites exchange and electron transfer mechanisms within COP-dechlorinating communities,and further proposed a detailed design,construction,and analysis framework of engineering COP-dechlorinating microbiomes via“top-down”selfassembly and“bottom-up”synthesis to pave the way from laboratory to practical field application.Especially,we delve into the major challenges and perspectives surrounding the design of state-of-the-art synthetic microbial communities.Our goal is to improve the understanding of the microbial-mediated coupling between reductive dechlorination and element biogeochemical cycling,with a particular focus on the implications for health-integrated soil bioremediation under the“one health”concept.

Electroluminescence from pure resonant states in hBN-based vertical tunneling junctions

Defect centers in wide-band-gap crystals have garnered interest for their potential in applications among optoelectronic and sensor technologies.However,defects embedded in highly insulating crystals,like diamond,silicon carbide,or aluminum oxide,have been notoriously difficult to excite electrically due to their large internal resistance.To address this challenge,we realized a new paradigm of exciting defects in vertical tunneling junctions based on carbon centers in hexagonal boron nitride(hBN).The rational design of the devices via van der Waals technology enabled us to raise and control optical processes related to defect-to-band and intradefect electroluminescence.The fundamental understanding of the tunneling events was based on the transfer of the electronic wave function amplitude between resonant defect states in hBN to the metallic state in graphene,which leads to dramatic changes in the characteristics of electrons due to different band structures of constituent materials.In our devices,the decay of electrons via tunneling pathways competed with radiative recombination,resulting in an unprecedented degree of tuneability of carrier dynamics due to the significant sensitivity of the characteristic tunneling times on the thickness and structure of the barrier.This enabled us to achieve a high-efficiency electrical excitation of intradefect transitions,exceeding by several orders of magnitude the efficiency of optical excitation in the sub-band-gap regime.This work represents a significant advancement towards a universal and scalable platform for electrically driven devices utilizing defect centers in wide-band-gap crystals with properties modulated via activation of different tunneling mechanisms at a level of device engineering.

The beauty of multi-active sites

The Sabatier principle—which states that the best catalyst should be at the peak of the volcano plot,with neither too strong nor too weak intermediate binding strength—plays the golden rule in designing highly active electrocatalysts.For instance,Pt with a“just right”hydrogen adsorption free energy(ΔG_(H^(*))=~0 eV)is the most efficient catalyst for hydrogen evolution reaction(HER).^(1)Nevertheless,the pressing demand for renewable energy has sparked a quest beyond the top of the volcano plot,driving the innovation towards more effective,economical.

Fast Bayesian optimization of Needle-in-a-Haystack problems using zooming memory-based initialization (ZoMBI)

Needle-in-a-Haystack problems exist across a wide range of applications including rare disease prediction,ecological resource management,fraud detection,and material property optimization.A Needle-in-a-Haystack problem arises when there is an extreme imbalance of optimum conditions relative to the size of the dataset.However,current state-of-the-art optimization algorithms are not designed with the capabilities to find solutions to these challenging multidimensional Needle-in-a-Haystack problems,resulting in slow convergence or pigeonholing into a local minimum.In this paper,we present a Zooming Memory-Based Initialization algorithm,entitled ZoMBI,that builds on conventional Bayesian optimization principles to quickly and efficiently optimize Needle-in-a-Haystack problems in both less time and fewer experiments.The ZoMBI algorithm demonstrates compute time speed-ups of 400×compared to traditional Bayesian optimization as well as efficiently discovering optima in under 100 experiments that are up to 3×more highly optimized than those discovered by similar methods.

Electrical manipulation of lightwaves in the uniaxially strained photonic honeycomb lattices under a pseudomagnetic field

The realization of pseudomagnetic fields for lightwaves has attained great attention in the field of nanophotonics.Like real magnetic fields,Landau quantization could be induced by pseudomagnetic fields in the strainengineered graphene.We demonstrated that pseudomagnetic fields can also be introduced to photonic crystals by exerting a linear parabolic deformation onto the honeycomb lattices,giving rise to degenerate energy states and flat plateaus in the photonic band structures.We successfully inspire the photonic snake modes corresponding to the helical state in the synthetic magnetic heterostructure by adopting a microdisk for the unidirectional coupling.By integrating heat electrodes,we can further electrically manipulate the photonic density of states for the uniaxially strained photonic crystal.This offers an unprecedented opportunity to obtain on-chip robust optical transports under the electrical tunable pseudomagnetic fields,opening the possibility to design Si-based functional topological photonic devices.

Relativistic domain-wall dynamics in van der Waals antiferromagnet MnPS_(3)

The discovery of two-dimensional(2D)magnetic van der Waals(vdW)materials has flourished an endeavor for fundamental problems as well as potential applications in computing,sensing and storage technologies.Of particular interest are antiferromagnets,which due to their intrinsic exchange coupling show several advantages in relation to ferromagnets such as robustness against external magnetic perturbations.Here we show that,despite of this cornerstone,the magnetic domains of recently discovered 2D vdW MnPS_(3)antiferromagnet can be controlled via magnetic fields and electric currents.We achieve ultrafast domain-wall dynamics with velocities up to~3000 m s^(−1)within a relativistic kinematic.Lorentz contraction and emission of spin-waves in the terahertz gap are observed with dependence on the edge termination of the layers.Our results indicate that the implementation of 2D antiferromagnets in real applications can be further controlled through edge engineering which sets functional characteristics for ultrathin device platforms with relativistic features.